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BACKPORT: dma-buf: Move dma_buf_release() from fops to dentry_ops

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Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which
happens if the dma_buf_release() is called while the userspace is
accessing the dma_buf pseudo fs's dmabuffs_dname() in another process,
and dma_buf_release() releases the dmabuf object when the last reference
to the struct file goes away.

I discussed with Arnd Bergmann, and he suggested that rather than tying
the dma_buf_release() to the file_operations' release(), we can tie it to
the dentry_operations' d_release(), which will be called when the last ref
to the dentry is removed.

The path exercised by __fput() calls f_op->release() first, and then calls
dput, which eventually calls d_op->d_release().

In the 'normal' case, when no userspace access is happening via dma_buf
pseudo fs, there should be exactly one fd, file, dentry and inode, so
closing the fd will kill of everything right away.

In the presented case, the dentry's d_release() will be called only when
the dentry's last ref is released.

Therefore, lets move dma_buf_release() from fops->release() to
d_ops->d_release()

Many thanks to Arnd for his FS insights :)

[1]: https://lore.kernel.org/patchwork/patch/1238278/

Fixes: bb2bb90 ("dma-buf: add DMA_BUF_SET_NAME ioctls")
Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org> [5.3+]
Cc: Arnd Bergmann <arnd@arndb.de>
Reported-by: Charan Teja Reddy <charante@codeaurora.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Tested-by: Charan Teja Reddy <charante@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200611114418.19852-1-sumit.semwal@linaro.org

Bug: 162699017

Signed-off-by: Allen Chiu <allen.chiu@mediatek.com>
Change-Id: Ief19296f201132c3e32b11958a857798c34f81fb
Git-commit: 2581e5be6555232e784487fc00961ce83c5236a1
Git-repo: https://android.googlesource.com/kernel/msm
Signed-off-by: PavanKumar S.R. <pavasr@codeaurora.org>
This commit is contained in:
Allen Chiu 2020-09-02 14:52:36 +08:00 committed by PavanKumar S.R
parent 46f5f96602
commit 7681a073f9
1 changed files with 22 additions and 27 deletions
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49
drivers/dma-buf/dma-buf.c
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@ -102,35 +102,12 @@ out:
dentry->d_name.name, ret > 0 ? name : "");
}
static const struct dentry_operations dma_buf_dentry_ops = {
.d_dname = dmabuffs_dname,
};
static struct vfsmount *dma_buf_mnt;
static struct dentry *dma_buf_fs_mount(struct file_system_type *fs_type,
int flags, const char *name, void *data)
{
return mount_pseudo(fs_type, "dmabuf:", NULL, &dma_buf_dentry_ops,
DMA_BUF_MAGIC);
}
static struct file_system_type dma_buf_fs_type = {
.name = "dmabuf",
.mount = dma_buf_fs_mount,
.kill_sb = kill_anon_super,
};
static int dma_buf_release(struct inode *inode, struct file *file)
static void dma_buf_release(struct dentry *dentry)
{
struct dma_buf *dmabuf;
struct dentry *dentry = file->f_path.dentry;
int dtor_ret = 0;
if (!is_dma_buf_file(file))
return -EINVAL;
dmabuf = file->private_data;
dmabuf = dentry->d_fsdata;
spin_lock(&dentry->d_lock);
dentry->d_fsdata = NULL;
@ -167,9 +144,28 @@ static int dma_buf_release(struct inode *inode, struct file *file)
module_put(dmabuf->owner);
dmabuf_dent_put(dmabuf);
return 0;
}
static const struct dentry_operations dma_buf_dentry_ops = {
.d_dname = dmabuffs_dname,
.d_release = dma_buf_release,
};
static struct vfsmount *dma_buf_mnt;
static struct dentry *dma_buf_fs_mount(struct file_system_type *fs_type,
int flags, const char *name, void *data)
{
return mount_pseudo(fs_type, "dmabuf:", NULL, &dma_buf_dentry_ops,
DMA_BUF_MAGIC);
}
static struct file_system_type dma_buf_fs_type = {
.name = "dmabuf",
.mount = dma_buf_fs_mount,
.kill_sb = kill_anon_super,
};
static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{
struct dma_buf *dmabuf;
@ -488,7 +484,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
}
static const struct file_operations dma_buf_fops = {
.release = dma_buf_release,
.mmap = dma_buf_mmap_internal,
.llseek = dma_buf_llseek,
.poll = dma_buf_poll,